Scientists terrify raccoons to reveal inner workings of ecosystems

Slightly weird experiment reveals how to stop a raccoon from wrecking everything in sight.

Raccoons may be adorable, but they have earned the nickname "trash pandas" for a reason. In cities, they'll knock over garbage bins to find food. In the wild, they take the same scorched-Earth approach to all the local wildlife they can fit in their mouths, wrecking ecosystems. Now, a group of scientists has figured out one way to stop them.

Off the coast of British Columbia, Canada, raccoons have invaded several of the Gulf Islands, with less-than-wonderful results. Though they were once kept in check by local bears, wolves, and cougars, these carnivorous predators have been eliminated by humans who viewed them as dangerous. The only natural predators of raccoons left on most islands are domestic dogs.

As a result, island raccoons are living it up—the nocturnal creatures are even coming out during the day to amble around on shore and eat. Raccoons are wolfing down coastal animals like crabs, worms, and fish at an alarming rate. They sometimes eat just part of a crab and then leave the rest of the body floating in the water. As a result, crab and other raccoon-prey species are being decimated.

Enlarge/ I'll eat this one, and this one, and this one and... oh, this one, too.

Marek C. Allen

It's all because the island ecosystems lack large carnivorous predators.

The researchers, who published the results of their study in Nature Communications, decided to test a hypothesis about the role of predators in an ecosystem. Obviously, large predators keep smaller predators like raccoons in check by eating or harassing them. But many environmental scientists believe that predators create an "ecology of fear" that restrains smaller animals, preventing them from gallivanting about like these island raccoons.

To test this hypothesis, the researchers decided to spend several months scaring the crap out of raccoons. They set up speakers along two sections of Gulf Island coastline and broadcast the sounds of dogs barking. To measure the effect this would have on raccoon behavior, they set up cameras. They also took samples to measure the population sizes of crabs and other favorite foods of the raccoons.

A naughty raccoon snoops around for food, then runs away when it hears the recording of a dog barking.

For controls, the researchers also took samples in coastal areas where they had broadcast non-predator noises, as well as areas where they had done no broadcasting at all.

Scarecrow tactics

What they discovered was that the raccoons who heard the menacing dog barks spent 66 percent less time foraging during the month, and many of them stopped venturing out to the coastline altogether. They were no longer boldly wandering the beach, eating little bits of one fish and little bits of another. They became more wary and took only the food they needed. Crab, fish, and worm populations quickly bounced back—at the end of the month, write the researchers, "there were 97% more intertidal crabs, 81% more intertidal fish, 59% more polychaete worms and 61% more subtidal red rock crabs." That's a major shift in the local ecosystem.

There are a number of interesting conclusions we can draw from this, not the least of which is that we now have evidence that scarecrow tactics can be part of ecosystem remediation strategies. In areas where predator loss has unraveled local food webs, it's possible to repair the damage just by making smaller predators like raccoons a lot more wary.

But there's also a larger point to be made here about animal consciousness.

Though it's commonly accepted that non-human animals have emotional lives, this study reveals that they are vulnerable to what you might call psychological warfare. For what is a broadcast dog bark if not a psychological tactic? The raccoons are in no literal danger. They are changing their behavior purely out of fear—in essence, they are having a psychological reaction.

Write the researchers:

The mere presence of large carnivores may therefore give rise to a ‘‘landscape of fear," buffering lower trophic levels from overconsumption by large herbivores and mesocarnivores [animals that eat mostly meat, like raccoons]. Failing to consider fear risks substantially underestimating the role large carnivores play, since fear may be as or more important than direct killing in causing trophic cascades.

Maybe it's time to consider that the animal kingdom is not ruled just by "tooth and claw," but also by more nuanced relationships. Humans are not the only creatures who have access to a life of the mind. We're just the only ones who write articles about it.